My boy was doing this too (and still tries) except he was pinching etc. we’ve weaned now though so I’m sure it has something to do with comfort/wanting boob still.
Mine tends to do thisnwhilst feeding he'll be on one side and hand in the other cup 😂
Yep she's even learnt the word boobie now too because of it 😂
My boy has started to pull my top out and look down at my boobs 😂. He also plays with my husbands nipples 😂